(unstack b3 b1)
(putdown b3)
(unstack b1 b4)
(putdown b1)
(unstack b4 b2)
(putdown b4)
(pickup b3)
(stack b3 b4)
(pickup b2)
(stack b2 b3)
(pickup b1)
(stack b1 b2)
; cost = 12 (unit cost)
